Depending on what day of the week, you could be through immigration and customs sooner than later. Passenger loads have started to go down from what I'm seeing and I'm not hearing about the long queues anymore as often.

Rush hour, I'd go Blue line over a cab going in, but late at night there's no reason you couldn't cab it back to the ORD hilton to save time.

May I ask what flight and day you're arriving on?